The Australian Transport Safety Bureau (ATSB) is Australia's national transport safety investigator. The ATSB's function is to improve safety and public confidence in the aviation, marine and rail modes of transport. The ATSB is Australia's prime agency for the independent investigation of civil aviation, rail and maritime accidents, incidents and safety deficiencies.

(b) discussions with Australian regional airline employees and
managers; and

(c) air safety occurrence reports in the BASI database involving
regional airlines over a 10-year period (1986 - 1995).

This interim recommendation addresses one of the safety
deficiencies identified as a result of this study.

Safety deficiency

The combining of air traffic service operator positions during busy
traffic periods can limit the ability of flight crew to exchange
essential position, emergency or traffic information.

Related Occurrences

BO9702957

A de Havilland Dash 8 and a Lockheed C130, travelling in opposite
directions on the same route, passed within 400 m of each other
while at the same level. Pilots of other aircraft operating on the
area frequency prevented the flight crews of the Dash 8 and the
C130 from communicating with each other in adequate time to arrange
separation. Two flight service positions were combined at one
console and there were reported to be 21 aircraft using the two
area frequencies, which were linked via a retransmission
facility.

BO9703696

The pilot in command (PIC) of a Beech B200 taxied at Smithton for
an IFR flight to Launceston. On departure he was unsuccessful in
establishing communications on 122.6 MHz to obtain traffic
information due to the volume of traffic on the frequency. The PIC
reported that the communications problem was due to the increased
traffic calls by aircraft taxiing at King and Flinders Islands,
visual flight rules (VFR) and instrument flight rules (IFR)
aircraft position reports and traffic requests for descent. The
problem was further exacerbated by the retransmit facility which
rebroadcast all transmissions on eight separate frequencies. The
pilot advised that he made six attempts before contacting Melbourne
to advise his departure, obtain traffic and to obtain a clearance
to enter controlled airspace.

Discussions with other pilots who operate in the same area and air
traffic service personnel in Melbourne, revealed that the frequency
congestion problems were most critical at weekends when frequencies
are combined.

BO9800106

At approximately 100 ft AGL after takeoff at Williamtown the left
engine on a Beech 1900D failed. The crew conducted emergency checks
and returned to the aerodrome and landed without further incident.
An emergency call to Sydney Flight Service was not possible due to
the large number of other pilots operating on the area
frequency.

Regional airline safety study

The results of the Regional Airlines Safety Study revealed that 72%
of respondents had experienced delays of more than two minutes due
to frequency congestion, while using flight service area
frequencies.

The study noted that frequency congestion appeared to be a problem
at a large number of locations across Australia, suggesting that
the problem was not isolated to one particular region.
Pilots'comments from the study indicated that congestion was worse
when frequencies were combined and particularly at weekends (when a
number a frequencies were usually combined and allocated to a
single operator position).

Reports since 1996

Reports since the study indicate that the problem of frequency
congestion is still occurring. However, it is now being experienced
on air traffic control frequencies since the transfer of some
flight service functions to air traffic control.

Equipment limitation

Aeronautical Information Circular H34/97 - Flight Information
Service Retransmission Facility, (December 1997) from Airservices
Australia, detailed an equipment limitation which can inhibit the
provision of services by air traffic services. The limitation was a
function of the retransmit facility used to network a number of
radio frequencies at an operator position. Airservices Australia
acknowledged the limitation and provided advice to assist pilots
operating on frequencies that may be retransmitted.

Analysis

Although Airservices Australia has endeavoured to address the
limitation inherent in the current equipment by issuing
Aeronautical Information Circular H34/97, more consideration of the
possible impact of the combining of air traffic service positions
is required.

Ready access to and use of the area frequency is essential for
crews of IFR flights to obtain traffic information from the air
traffic service operator. Ready access to the area frequency is
also essential for the exchange of position information between the
crews of IFR and VFR flights, in order for an assessment of
potential conflict to be made. The combining of two or more area
frequencies using retransmission may create a hazard for aircraft
operations.

Airservices Australia should develop procedures to assist operators
in evaluating the advantages of combining air traffic service
positions against the consequent potential for frequency congestion
and the possibility of a degradation of safety in the aviation
system.

Output text

The Bureau of Air Safety Investigation recommends that
Airservices Australia review air traffic service procedures
relating to the combining of a number of operator positions and/or
frequencies with a view to reducing the impact of frequency
congestion.

Initial response

Initial response

Date issued:

11 November 1999

Response from:

AirServices Australia

Action status:

Open

Response text:

Reference is made to BASI's Air Safety Interim Recommendation
No: IR 980059 regarding the use of ATS frequencies.

In addition to AIC H34/97, Airservices provides direction to ATS
staff regarding the use of retransmit facilities in MATS 12-4-2
which shows "To reduce frequency congestion and interference on
pilot broadcasts or other pilot-to-pilot communications being used
for self separation, the retransmit facility should be operated in
the "OFF" mode whenever practicable".

A number of other factors, in the context of the Airspace 2000
initiatives, relating to the provision of services are currently
being discussed with CASA. Implementation of aspects of these
initiatives would affect not only the way services are provided but
the way in which ATS frequencies are used.

Airservices will continue to monitor the effects of retransmit
facilities pending resolution of a number of issues associated with
the implementation of CASA's Airspace 2000 initiatives.

ATSB response:

The following letter was sent to Airservices Australia on 6
December 1999:

Subject: Outstanding airspace related safety actions

Responses to some previous safety recommendation to Airservices
Australia and the Civil Aviation Safety Authority (CASA) proposed
actions that were subject to the latter's Airspace 2000 initiative
or the resolution of related issues.

Since the Minister of Transport and Regional Services' statement
clarifying the roles and responsibilities for airspace management
it has become apparent that, with the change in roles, CASA may not
be in a position to implement all of their proposed airspace
related safety actions. Consequently, there is the likelihood that
there will be less safety enhancement of airspace than there
previously might have been.

However, should Airservices Australia review the safety
recommendations previously forwarded to CASA and the subsequent
responses, during the development of the new airspace project, the
knowledge gained from past air safety investigations has the
potential to be retained. Consequently,the ATSB would appreciate
Airservices consideration and advice of any subsequent proposed
action, of interim recommendation (IR) 19970155 issued on 30
January 1998 and the CASA response of 25 August 1999 (both
attached).

Similarly, advice of any proposed action in regard to
IR19960009, IR19980005 and IR19980059 issued to Airservices, where
further action was also subject to CASA's Airspace 2000, would
assist the ATSB in understanding the integration of safety lessons
with future airspace
developments.

Further correspondence

Further correspondence

Date issued:

11 July 2000

Response from:

AirServices Australia

Response status:

Closed - Accepted

Response text:

I apologise for the late response to your letter dated the 6th
of December 1999, concerning the resolution of matters relating to
the Airspace 2000 initiative. We note the recent statement by the
Minister for Transport and Regional Services, and its effect in
clarifying the roles and responsibilities for airspace
management.

In the current airspace management arrangements, Airservices
holds the legislative responsibility for the declaration of
airspace in accordance with the ICAO "alphabet" menu of airspace.
Responsibility for procedures applicable within airspace classes,
including Class G airspace, together with ongoing training and
pilot education remains with the Civil Aviation Safety
Authority.

In that context, we believe that Recommendation IR19970155,
relating to separation assurance in Class G airspace is more
properly directed to CASA.

In relation to Recommendations IR19960009, IR19980005 and
IR19980059, I offer the following advice:

IR19980059: Whilst Airservices disagrees in part with the
investigation report, the recommendation is accepted.

During the transition to TAAATS, Safety Cases have been
conducted. These Safety Cases include consideration of a variety of
hazards, including frequency congestion. This is particularly the
case in relation to the current initiatives to absorb the provision
of Directed Traffic Information services into TAAATS.

In relation to your statement regarding the integration of
safety lessons with future airspace developments, Airservices is
acutely aware of the primacy of safety in all aspects of our
operations. In work being undertaken with industry to achieve
reforms in the provision of services in low level airspace,
detailed examination of hazards, potential mitigations, safety
analysis and risk modelling are a fundamental part of our
considerations. We would welcome the opportunity to provide you and
your staff with a